The present invention relates generally to the stabilization of pigments against sunlight-induced bleaching and, in particular, relates to such stabilization of the pigment rubrolone.
Rubrolone is a water-soluble amorphous red solid of microbial origin having the emirical formula C.sub.23 H.sub.23 NO.sub.8 and the following structural formula: ##STR1## 8(R), 9(R), 10(S), 10a(R)-tetrahydro-9,10,10a,11-tetrahydroxy-3,8-dimethyl-1-propyl-6aH(S)-py rano[2",3":5',4]furo[2',3':5,6]azuleno[2,3-c]pyridine-5,13-dione.
The preparation and structural analysis of rubrolone is described in Palleroni, et al., The Journal of Antibiotics, vol. 31, no. 12, p. 1218 (1978); Schuep, et al., The Journal of Antibiotics, vol. 31, no. 12, p. 1226 (1978); and U.S. Pat. No. 4,057,533.
Although the significant water solubility of rubrolone makes it attractive as a colorant for foods, and particularly for water-based products such as beverages, we have found that rubrolone undergoes degradation upon direct exposure to sunlight with a resultant color loss in products colored therewith.